Menarche is the culmination of a series of central nervous system maturational events. In normal girls, the time course from menarche to the establishment of regular, ovulatory cycles is only partially studied. Prior studies have been limited by the need to use serial serum sampling and inadequate sampling frequencies to determine definitively whether or not ovulation occurs. Recent clinical research indicates that, in a population of normal young women, regular cycles are established relatively rapidly (i.e., within a year) of menarche. However, this and other studies have been unable to elucidate the patterns of menstrual cycling that occur up to and after the onset of menstruation. It is the broad goal of this proposal to describe the pattern(s) of reproductive hormones in normal girls at menarche and to determine the latency to regular, ovulatory cycling in normal perimenarcheal girls. This overall goal will be accomplished using the K24 award mechanism to develop further the career of the PI while providing mentorship, guidance and focus for a junior faculty member within the Department of Ob/Gyn and Women's Health at the Albert Einstein College of Medicine (AECOM). The three specific aims of the proposal are to: 1. Provide protected time for the PI to obtain formal training in epidemiology and biostatistics; 2. Undertake a mentored research experience for Dr. Staci Pollack, a junior faculty member in the Department of Ob/Gyn and Women's Health; and 3. Develop a new line of research that will address unanswered questions about the maturation of the hypothalamic-pituitary-axis in peripubertal girls. These aims will be achieved concurrently by the enrollment of Dr. Santoro in the Clinical Research Training Program at the AECOM's epidemiology and biostatistics courses in Years one and two of the project period. At the time Dr. Santoro is acquiring this expertise, Dr. Pollack, her trainee and protege, will implement a study of perimenarcheal reproductive hormonal dynamics in a population of girls. Dr. Santoro will mentor Dr. Pollack in the laboratory techniques of field assessments of urinary hormone patterns and their analysis, an area in which she has experience and a substantial track record. Dr. Pollack and Dr. Santoro will complete the funding period with the development and initiation of preliminary data and study design sufficient to fund a larger clinical trial that will address some of the causes of reproductive endocrine abnormalities in perimenarcheal girls.